The present invention relates to an apparatus for controlling a brake means of a vehicle which includes an automatic transmission, a shift lever, an engine and a brake means.
More particularly, the present invention relates to the apparatus for controlling the brake means when the automatic transmission is manually operated.
A conventional hydraulic control type automatic transmission includes brakes, clutches and epicycle reduction gears. When the conventional automatic transmission converts drive position, the brakes and the clutches are selectively engaged or disengaged, as a result, the gear ratios of the epicycle reduction gears are changed.
When a fourth drive position of a drive range "D" is converted into a second drive position of a second range "2", as shown in FIGS. 1-A and 1-B, the brake, frictioning as an engagement elements, is actuated.
The hydraulic pressure of the brake "Bo" is reduced at time "Ta" when converting from the fourth drive position of the drive range "D" into the second drive position of the second range "2" as indicated, and the hydraulic pressure of the clutch "Co" is increased to achieve a temporary third drive position.
Next, in the temporary third drive position, the hydraulic pressure of the clutch "C2" is reduced at time "Td", and hydraulic pressure of the brake "B1" is increased to achieve a second drive position of the second range "2" (i.e., in the condition of the converting of drive position, first of all, the brake "Bo" is disengaged and the clutch "Co" is engaged. Next, the clutch "C2" is disengaged and the brake "B1" is engaged.)
However, when the conventional automatic transmission is operated manually to obtain an engine brake function, there are various problems caused by the conventional automatic transmission during the converting of drive position (i.e., there are neutral conditions during time periods defined between "Tb" and "Tc", and between "Te" and "Tf"). In the neutral conditions, as shown in FIG. 1-A, output shaft torque of the automatic transmission becomes almost zero. The neutral condition is a result of the piston strokes of the clutch and the brake. In order to shorten the neutral condition, the piston stroke of the brake was shortened. However, if the piston stroke of the brake were too short, the brake would function always in normal driving condition.
On the other hand, when the fourth drive position of the drive range "D" is converted into the second drive position of the second range "2", first of all, the fourth drive position of the drive range "D" is converted into the temporal third drive position (i.e., a third drive position converting), and then the temporal third drive position is converted into the second drive position of the second range "2" (i.e., a second drive position converting).
Thus, in order to prevent the second drive position from converting simultaneously during the third drive position converting, it is designed that the second drive position converting starts later than the third drive position converting.
Accordingly, as described above, the conventional automatic transmission has problems (e.g., there is a neutral condition during time periods defined between start of the converting of drive position and start of engagement of the brake).
As a result, if the shift lever of the conventional automatic transmission were manually operated to obtain the engine brake function (e.g., when the vehicle drives down a steep hill) the vehicle would be accelerated. In other words, when an operator operates the conventional automatic transmission to obtain the engine brake function, the vehicle is accelerated regardless of the intention of the operator because of the neutral conditions of the conventional automatic transmission.